EXPERIMENTS ON BIRD MALARIA 389 



throat. Compounds which are very toxic can often be given in 

 greater amounts without poisoning the bird if the dose is frac- 

 tionated. The time of treatment may also be of some importance 

 since the parasites are assumed to be more vulnerable to the 

 action of toxic drugs during the period of sporulation. 



If desired, drugs can be quite easily administered by injection. 

 Intramuscular and subcutaneous injections can be most readily 

 performed in the region of the breast because of the scarcity of 

 feathers in this part of the body. The method of making an intra- 

 muscular injection into the breast muscle has already been de- 

 scribed. Intraperitoneal injection is almost as convenient, and 

 intravenous injection can be done if desired. The technique for 

 this has already been given. It is of course always essential to 

 see to it that the solutions injected are isotonic with the blood, 

 and it is also well to have them warmed to about 40° C. 



17. Measuring the effect of drugs. The effect of drugs or of 

 other agents upon the course of the infection may be measured in 

 various ways, depending somewhat on when the treatments are 

 given. The author has always believed that the efifect could best be 

 gauged by changes in the length of the prepatent period. If this is 

 to be the index of success, the treatment must be commenced very 

 soon after the initial inoculation of the parasites, and daily blood 

 smears must be made until these are found. Any substance which 

 tends to lengthen the prepatent period may be assumed to exert a 

 curative efifect, and vice-versa. 



If the drug is not administered until parasites can be demon- 

 strated in the blood then its effect can be measured either by mak- 

 ing daily counts of the number of parasites per unit number of 

 red cells (in practice 10,000 has been found a very convenient 

 unit), or by making polar planimeter determinations of the areas 

 of the parasites at dift'erent periods during the course of the treat- 

 ment. The latter method was devised by Hartman (unpublished 

 report). This worker (1927) found however that as the number 

 of parasites increased a progressive decrease could be noted in 

 their size, quite irrespective of any treatment, so that this factor 

 must be taken into account. It is not very practical to make daily 

 counts of the red cells, or of the parasites contained in them, be- 

 cause the amount of blood in a normal canary bird is not much 

 greater than one cubic centimeter and during the course of a 

 malarial infection there is a very severe anemia. It is of course 



